Plenty of countries with land borders have sensible gun control.
..and it's just as ineffective there, just look at France.
In Australia you can already buy guns illegally. Criminal gangs have guns, but they tend to use them to settle scores rather than against the non-gang population.
Dittos in the US, most of the murders are gang related. Almost 50% of firearm homicides are black men killing other black men.
You can also make all sorts of offensive weapons already, but this is not a widespread practice because it's illegal and shit and you can get into a lot of trouble for making or having bombs and other homemade weapons.
Again, this is the same as the US.
The argument that new technologies will result in an explosion in the number of unregistered guns being made is similar to fears a few years back that the availability of high quality colour printers would result in uncontrollable widespread counterfeiting operations. How did that turn out? People who print fake money are traceable and are punished. People who illegally make guns at home... ditto.
This is a piss poor comparison. In the case of counterfeit money, the criminal is giving it out to non-criminals where it is quickly discovered and some good police work can trace it back to its source. With guns, either the criminals keep them or they sell them to people they think they can trust. Since the distribution is so tight, it's difficult to trace where they came from since only one or two guns will be discovered at a time.
Gun culture and a large (and influential) gun manufacturing industry... certainly unique to the United States, at least among first world countries. You guys want to keep your guns and keep shooting each other, that's fine by me. Just don't expect me to agree that it's a great idea.
The overwhelming majority of legal gun owners don't shoot each other, the majority of shootings are criminals shooting other criminals.
